The juice of a small tree of the Acacia tribe, growing in Egypt, Arabia Petræa, Palestine, and in different parts of America.
Are there other plants or trees which produce Gum, besides those already mentioned?
A great number, though not all commonly in use. The leaves of rhubarb, the common plum, and even the sloe and the laurel, produce a clear, tasteless gum; there are also a number of different gums, brought from foreign countries, of great use in medicine and the arts. Most of the Acacias produce gums, though the quality of all is not equally good.
What is Rhubarb?
A valuable root growing in China, Turkey, and Russian Tartary. Quantities of it are imported from other parts of the world: that from Turkey is esteemed the best. Rhubarb is also cultivated in our gardens, and the stalks of the leaves are often used in tarts; but the root, from the difference of climate, does not possess any medicinal virtue.
CHAPTER XII.
Spectacles, Mariner's Compass, Barometer, Thermometer, Watches, Clocks, Telescope, Microscope, Gunpowder, Steam Engine, and Electro-Magnetic Telegraph.
When were Spectacles invented, and who was their inventor?
It is supposed that they were first known about the thirteenth century, and invented by a monk of Pisa, in Italy, named Alexander de Spina. Spectacles are composed of two circular pieces of glass set in a frame.